1. Technical Field of the Invention
This invention relates to a substrate processing apparatus and method, more particularly, relates to a substrate processing apparatus and method useful for forming embedded interconnects that an electric conductor, such as copper or silver, is embedded in fine recesses for interconnects formed in the surface of a substrate like a semiconductor substrate, and for forming a protective layer for protecting the surface of the interconnects.
2. Description of the Related Art
An electroless plating is such a method that a plated film is formed on a plating surface of a workpiece by chemically reducing metal ions in a plating solution without supplying any electric current from the outside, and the electroless plating is widely used in a nickel-phosphorus plating and a nickel-boron plating for giving a corrosion resistance and a wear resistance, and a copper plating for a printed-wiring substrate.
As an electroless plating apparatus, there has been generally known an apparatus comprising a plating bath for holding an electroless plating solution which overflows during plating process, and a vertically movable holding portion disposed above the plating bath for holding a plating workpiece, such as a substrate, whereby the workpiece held by the holding portion is dipped into the plating solution in the plating bath.
In recent years, as the processing speed and integration of a semiconductor chip becomes higher, there has been a growing tendency to replace aluminum or aluminum alloy with copper having a low electric resistivity and a high electromigration resistance as metallic materials for forming interconnection circuits on the semiconductor substrate. These kinds of copper interconnects are generally formed by filling fine recesses formed in the surface of the substrate with copper. As a method for forming the copper interconnects, CVD, sputtering, and plating are known, but plating is generally used. In any case, after a copper film is deposited on the surface of the substrate, the surface of the substrate is polished to a flat finish by chemical mechanical polishing (CMP) process.
In the case of interconnects formed by such a process, the embedded interconnects have an exposed surface after the flattening processing. When an additional embedded interconnect structure is formed on such an exposed surface of interconnects of a semiconductor substrate, the following problems may be encountered. For example, during the formation of a new SiO2 interlevel dielectric, the exposed surface of the pre-formed interconnects is likely to be oxidized. Further, upon etching of the SiO2 layer for the formation of contact holes, the pre-formed interconnects exposed at the bottoms of the contact holes can be contaminated with an etchant, a peeled resist, etc. Moreover, in the case of copper interconnects, there is a fear of copper diffusion.
In view of this, in the case of copper interconnects, for example, it may be considered to selectively cover the surface of copper interconnects with a protective layer (plated film) of a Ni—B alloy or the like, having a good adhesion to copper and a low resistivity (ρ). The Ni—B alloy layer can be formed on the surface of e.g. copper selectively by using an electroless plating solution that contains nickel ions, a complexing agent for nickel ions and an alkylamine borane or a borohydride compound as a reducing agent for nickel ions and by immersing the surface of the substrate in the electroless plating solution.
An electroless plating is applied to main filling materials (Cu) for the copper interconnects, the formation of the seed layer on the barrier metal, or the reinforcement of the seed (Cu), further the formation of the barrier metal itself, or the formation of cap material for the copper interconnect (in any case, Ni—P, Ni—B, Co—P, Ni—W—P, Ni—Co—P, Co—W—P, Co—W—B), or the like. In any electroless plating process, uniformity of the film thickness over an entire surface of the substrate is required.
In electroless plating, when a plating surface of a workpiece is brought into contact with an electroless plating solution, a plating metal instantly begins to deposit on the plating surface of the material, and the deposition rate of the plating metal varies depending on the temperature of the plating solution. Accordingly, in order to form a plated film having a uniform film thickness over the plating surface of a workpiece, the temperature of a plating solution is required to be uniform all over the surface of the material from the initial time of contact between the workpiece and the plating solution, and the uniform plating temperature must be kept throughout the plating treatment.
In order to meet this demand, conventional electro less plating apparatuses are generally designed to perform plating in such a manner that the plating surface of a substrate is allowed to be in contact with a plating solution which has previously been heated to a predetermined temperature, and the substrate and the plating solution are heated (kept warm) during plating by means of a heater, a lamp, or the like in order to maintain the plating temperature. Further, with a view to obtaining uniformity of the plating temperature, the conventional electroless plating apparatuses generally employ the so-called one-by-one processing method of processing one substrate in one plating processing. Also with substrate processing apparatuses for carrying out processing incidental to plating, such as pre-plating processing and post-plating cleaning, because of the one-by-one plating processing, the one-by-one processing method has conventionally been employed.
Such conventional substrate processing apparatuses, which employ the one-by-one processing method, necessarily involve the problem of poor throughput. Further, as described above, a conventional electroless plating apparatus needs the provision of a device for heating (keeping warm) substrate or a plating solution. In the case of a pre-plating processing apparatus of a spray type, incidental equipments, such as pressure pump, a nozzle and a pipe, are needed. The conventional substrate processing apparatuses are thus likely to be complicated, leading an increased production cost.
The above and other objects, features, and advantages of the present invention will be apparent from the following description when taken in conjunction with the accompanying drawings which illustrates preferred embodiments of the present invention by way of example.